Jackson U.S. Pat. No. 4,054,469 is directed to a series of directionally solidified eutectic .gamma.+.beta. nickel base superalloys which contain not only chromium and aluminum, but also iron and/or cobalt. The patent further calls for a number of other elements such as B,W, Mo and Zr. The Zr is apparently a tramp element ranging from 0 to 0.1 weight percent. The patentee is concerned with improving the cyclic oxidation resistance of this nickel base superalloy. However, cyclic oxidation resistance is in no way indicated as being related to any spall inhibitor, such as Zr, and no discussion is set forth on optimizing the composition of the Zr.
Baldwin U.S. Pat. No. Re. 29,920 relates to a nickel base superalloy that is similar to that set forth in Jackson U.S. Pat. No. 4,054,469. However, the aluminum content of the alloy is only up to eight percent. Also, the patent lists many other constituents which are present in the alloy.
British Pat. No. 1,001,186 to Sands et al. is also directed to a nickel base superalloy that is quite similar to that of the two aforementioned patents. The aluminum content can be as high as 10 percent, and the alloy can be employed in powder metallurgy. Here again, this alloy of the British patent contains many other constituents.